Wide range power combiner

ABSTRACT

A wide range power combiner (WRPC) includes an electronics system that combines power from a plurality of input sources, which can differ in level, to at least a single output. In certain embodiments, a circuit can be constructed as shown in the figures (FIG.  1 ); a controller is used to generate a control signal to the switches, and for monitoring the energy storage elements. A possible control signal to the switches is shown in the figures (FIG.  2 ). The control signal, or signals, can dynamically change the frequency and order of switching to cause the switches to change the electrical connections of the energy storage elements, between the input and the output or outputs. A possible dynamic control algorithm is shown in the figures (FIG.  4 ). Switches can be any electrical switch, including transistors and relays. Energy storage elements can be any energy storage element, including capacitors and inductors.

TECHNICAL FIELD

The present disclosure relates to the combination of multiple DC powersources, and more particularly to the combination of multiple DC powersources that have different voltage, current, or maximum power points,into at least a single output.

BACKGROUND ART

Combining multiple power sources of different voltages or currentsefficiently can be a challenge in the field of electronics. When powersources are combined in series, they may not have the same current atthe maximum power point, and since the current must be equal across allsources, one or all will not be operating at their respective maximumpower point. Alternatively, if power sources are combined in parallel,they may not have the same voltage at the maximum power point. Since thevoltage across all power sources must be the same in a parallelconfiguration, some or all of the power sources may not be operating attheir respective maximum power point.

Various topologies have been developed to connect multiple power sourcesto a load, and fall under several categories. One category is theindividual control and regulation of each power source, of which oneexample is in the Patent Literature 1. Each power source has a maximumpower point tracking (MPPT) module connected to it, with the outputs ofthe MPPT modules connected together. The output voltage of the each MPPTmodule is regulated to the output of the string. Various topologies forthe MPPT modules, various control methods, and various connectionsbetween MPPT modules exist.

Another method to combine power sources is to connect them togetherthrough a transformer, with each power source having windings around acommon core. This method is fundamentally a buck-boost type dc-dcconverter system with the inductor being substituted with a transformer,which has multiple input windings. An example of one such system isdescribed in the Non Patent Literature 1. There are variousimplementations of this system, which have different configuration ofthe windings, DC-DC regulation, and control systems.

CITATION LIST Patent Literature

[PTL 1] PCT patent application No. PCT/US2013/064477

Non Patent Literature

[NPL 1] H. Matsuo et al., “Characteristics of the Multiple-Input DCDCConverter,” IEEE Trans. Ind. Electron., vol. IE-51, pp. 625-631, June2004.

DISCLOSURE OF INVENTION

A system for the combination of multiple input power sources into atleast a single output is provided. The electronics system maximizes thepower of the output or outputs, from a plurality of input power sources.In certain embodiments, the electronics system may be used with anysuitable power source at the inputs, including photovoltaics, windturbines, and batteries. The electronics system is able to detect thepower produced by each power source, intelligently monitor the input,and switch the configuration of energy storage elements. The switcheschange the electrical connections of the energy storage elements betweenthe input and the output or outputs. The system operates in order toobtain the maximum power from each of the sources, for any environmentalconditions.

The advantages of using this system may be to provide an alternative toconnecting power sources in series or parallel, that vary in voltage orcurrent output, in order to avoid power losses. This advantage may beobserved when the system is used with photovoltaics, where sources ofinefficiency, including uneven cloud cover, can cause the power outputsof a plurality of cells to be mismatched. The advantages of this systemover the current art include the decreased number of components, designsimplicity, and the absence of expensive components such as transformersor inductors.

The WRPC system comprises a plurality of power sources, the electronicsswitching system, the energy storage elements, measurement device(s),and the controller. The controller is used to control switches and takemeasurements from the energy storage elements.

In some embodiments, the controller is an intelligent controller thatutilizes control algorithms. The controller monitors input from theenergy stored in the energy storage elements, and the controllerintelligently switches the configuration of the connections of theenergy storage elements, between the input power sources and the outputor outputs, in such a way as to ensure the maximum power output fromeach source.

In some embodiments, the method of operation of the device is that eachpower source has two energy storage elements which are charged by thepower source. Each energy storage element has an input switch connectingit to its power source, and an output switch connecting it to the outputor outputs. The system can disconnect any one of the energy storageelements from the power source to connect it to the output. While one ofthe energy storage elements is connected to the output, the power sourcecontinues to charge the other energy storage element(s). The other powersources whose energy storage elements are not connected to the output,continue to charge both energy storage elements. In some embodiments,more than two energy storage elements per power source may be used. Insome embodiments, an energy storage element can be used at the output tosmooth variances in the voltage.

In some embodiments, the controller will use information about theamount of energy stored in the energy storage elements to determine thecharge rate of the elements. The maximum power point of the source isfound by searching for the voltage that produces the highest charge rateof the energy storage elements. This is carried out such that the searchspace is within the tolerances of the energy storage elements and theswitching system, and the maximum and minimum desired output power orvoltage.

In some embodiments the switches are controlled in such a way that theinputs are isolated from one another through time division multiplexing.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a block diagram of an embodiment of the wide rangepower combiner (WRPC) switching system.

FIG. 2 Illustrates one period of an unoptimized switch timing diagram,where each energy storage element is individually connected to theoutput, in sequence.

FIG. 3 Illustrates an example of the maximum power point of an inputpower source to the wide range power combiner (WRPC)

FIG. 4 Illustrates a block diagram of an intelligent control algorithmthat can be utilized by the controller, to control the wide range powercombiner (WRPC) switching system.

BEST MODE OF CARRYING OUT INVENTION

Embodiments of the invention are described more fully hereinafter withreference to the drawings.

In some embodiments the switches may be transistors, and the energystorage elements may be capacitors.

In the case of two energy storage elements per power source, as shown inFIG. 1, each storage element is connected to the power source through aninput switch. Each switch is controlled independently by the controller.When the switch between the power source and the capacitor is closed theenergy storage element will be charged by the power source.

Every storage element is also connected to the output through a switch.When the energy storage element is being charged from the power source,the output switch will be open, and the energy storage element will bedisconnected from the output. When an energy storage element isconnected to the output, the input switch will be open, and the energystorage element will be disconnected from the power source. While theenergy storage element is providing power to the output, the powersource continues to charge the second energy storage element. Only oneenergy storage element is connected to the output at a time.

Due to limitations of MOSFETs, proper considerations need to be taken toensure that no current is conducted between energy storage elementsacross different input power sources.

The timing of the switches is controlled by a controller. In someembodiments the controller can be a micro controller. The controller cancontrol the switches using a timing diagram as in FIG. 2, where oneperiod of switching is shown, or the controller can utilize anintelligent control algorithm to ensure efficient operation and ensuringthat each input power source is operating at its maximum power point. Acontrol algorithm is described below.

The energy in the capacitors is measured by measuring the voltage, andusing the known capacitance according to the formula:

E=½*C*V2

Where E is the total energy stored in Joules, C is the capacitance ofthe capacitor in Farads, and V is the measured voltage in Volts. Thechange in energy in the energy storage element(s) would be equal to theoutput power of the power source. This can be used to determine themaximum power point of the power source, because as the voltage of thecapacitor increases, the rate of charge will also change as shown inFIG. 3.

Once the maximum power point of the source is found, the controller willintelligently select the energy storage element which must be connectedto the output. This selection is made to ensure that the voltage of eachenergy storage element remains at the voltage of the maximum power pointof its input power source. An example of such a control algorithm isshown in FIG. 4.

In the control algorithm of FIG. 4, an energy storage element isselected, and if it has not yet been measured, the voltage of theselected energy storage element is measured. This is repeated until thevoltage of all energy storage elements have been measured. Next, thedifference between the voltage of each storage element and the voltageat the maximum power point of its source is determined. The energystorage element that is currently connected to the output isdisconnected, and then connected to its power source. The energy storageelement with the largest difference, that also has a greater voltagethan that of the maximum power point of its input power source, is thendisconnected from its power source and connected to the output. Allstored measurement values are cleared and the controller begins theprocess of selecting the next energy storage element, to connect to theoutput, from the beginning.

A dynamically changing load can be used at the output of the wide rangepower combiner (WRPC) to ensure that all input power sources areoperating at their maximum power point. A DC-DC converter can be used todynamically change the apparent output load of the wide range powercombiner. A DC-DC converter can be a boost converter. If the boostconverter is intelligently controlled, at a frequency that is relativelyhigh in comparison to that of the switching frequency of the WRPCswitching system, it can adapt to the changes in the WRPC output. Theuse of the DC-DC converter at the output of the WRPC can provide a fixedDC output voltage.

What is claimed is: 1) A wide range power combiner (WRPC) systemcomprising: a plurality of input power sources; a set of energy storageelements, with at least two energy storage elements per power source,such that each of the energy storage elements can be connected to apower source or an output or outputs; a set of switches, connecting theenergy storage elements to the input power sources and the output(s); atleast one measurement device, for the measurement of energy storageelements; a controller comprising: a control loop for the system,wherein the control loop learns the maximum power point for each powersource, and connects and disconnects different storage elements to andfrom the system output; systems constraints for managing limitations tomaintain energy output, voltages, currents, and other variables withinsystem parameters. 2) The WRPC system in claim 1, where the energystorage elements are provided in at least a 2:1 ratio of storageelements to power sources. 3) The WRPC system in claims 1-2 where theenergy storage elements are substantially identical. 4) The WRPC systemin claims 1-3 where input power of each source is controlled to achievethe maximum power point of that source 5) The WRPC system in claims 1-4where in maximum power point is detected automatically by the systemcontroller. 6) The WRPC system in claims 4 and 5 where the controller isconfigured to measure the energy stored in the energy storage elements,to determine the output power of the power sources. 7) The WRPC systemin claim 6, where the controller uses voltage measurements and theproperties of the energy storage element to calculate the energy storedin the energy storage element. 8) The WRPC system in claims 1-7 whereall but one of the energy storage elements are each connected to theirrespective input power sources, and all but one of the input powersources each being connected to at least two energy storage elements. 9)The WRPC system in claims 1-8 where the controller selects which energystorage element to connect to the output, in order to maintain themaximum power point of each input power source.